by
Bittinger, Marvin L.; Ellenbogen, David J.; Johnson, Barbara L.

Answer

17

Work Step by Step

The opposite of a real number $a$ is $-a$.
For any two numbers $a$ and $-a$, $a+(-a)=0$. That is, the sum of a number and its opposite is equal to 0.
Therefore, the opposite of -17 is 17, because $-17+(17)=17-17=0$.